Belt grinding machine tool with device for controlling the position of the abrasive belt

ABSTRACT

A belt grinding machine tool with an operating head comprising an endless abrasive belt wound and stretched between at least two spaced rollers arranged parallel one another, of which a first is a driving roller and a second is a tensioning roller being supported to be adjustable in a direction which is substantially perpendicular to its axis of rotation. A device is provided for controlling the position of the abrasive belt which consists of at least a position sensor for sensing the position of the abrasive belt and at least an actuator for adjusting the position of the tensioning roller, in dependence of the position of the abrasive belt being sensed by the position sensor. The position sensor is a fork shaped optical sensor, or an optical sensor having an operatively equivalent shape, and the actuator is an electric drive.

TECHNICAL FIELD

The present invention generally relates to the technical field of machine tools for processing the surfaces of plate- and/or strip-shaped workpieces and, in particular, concerns a belt grinding machine tool of the type provided with an operating head either for calibrating and/or sanding operations or for surface finishing and/or grinding operations, and comprising a device for controlling the position of the abrasive belt.

BACKGROUND

In machine tools of the type mentioned above it is known to use an automatic device to keep the grinding belt in position while it rotates and to prevent possible deviations of the grinding belt from its path of movement and consequent damage thereto, caused by an impact against the machine members and/or parts on which the belt is mounted.

Generally, the abrasive belt is mounted on an operating head which may exhibit various configurations, but which, however, is provided with a so-called “tensioning” roller, the position of which is adjustable by means of a suitable automatic device to allow for proper positioning of the abrasive belt.

The automatic device usually consists of a pneumatic actuator which is connected to the tensioning roller and is arranged in such a way to allow the position of one of the roller supports to be adjusted in a direction which is perpendicular to the axis of rotation of the roller.

The position of the tensioning roller is adjusted by means of the pneumatic actuator, in dependence of the position of the abrasive belt being sensed by one or more position sensors, for example of the type comprising a photoelectric cell.

An automatic device of the type mentioned above exhibits, in general, some disadvantages which combine to limit, in one aspect, the range and precision of controlling the position of the abrasive belt, and to increase, in another aspect, the ineffectiveness in controlling the path of movement of the abrasive belt and, therefore, the risk of damage thereto caused by impacts against members and/or parts of the machine on which it is mounted. It is, therefore, task of the present invention to obviate these drawbacks of the known devices for controlling the position of the abrasive belt of a belt sanding or calibrating machine, or the like.

DISCLOSURE OF THE INVENTION

More in particular, in accordance with the invention, the task mentioned above is accomplished by means of a belt grinding machine tool with an operating head comprising an endless abrasive belt wound and stretched between at least two spaced rollers arranged parallel one another, of which a first is a driving roller and a second is a tensioning roller, said tensioning roller being supported to be adjustable in a direction which is substantially perpendicular to its axis of rotation, a device for controlling the position of said abrasive belt consisting of at least a position sensor for sensing the position of the abrasive belt and at least an actuator for adjusting the position of the tensioning roller, in dependence of the position of the abrasive belt being sensed by said position sensor, wherein the position sensor is a fork shaped optical sensor, or an optical sensor having an operatively equivalent shape, and said actuator is an electric drive.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail with reference to a preferred embodiment thereof, illustrated in the attached drawings, wherein:

FIG. 1 is a schematic and partial view of the operating head of a belt grinding machine according to the invention, shown therein in transverse cross-section, and

FIG. 2 is a longitudinal partial cross-section of the operating head of FIG. 1.

DETAILED DESCRIPTION

The present invention is applicable generally to any type of belt grinding machine having an operating head either for calibrating and/or sanding operations or for surface finishing and/or grinding operations. It is also applicable to a belt grinding machine equipped with an operating head which operates either with or without water, oil or water/oil emulsion coolant, and which may be built in the “top” or “bottom” variant, with regard to the position of said operating head relative to the surface of the workpieces to be machined.

For the sake of brevity of the description, the possible applications of the invention to all types operating heads of belt grinding machines will not be described in the following, but for exemplification and non-limiting purposes the description will refer only to the application to the most simple and well known type of operating head, which is illustrated in FIG. 1 of the drawings and is designated therein by 10.

The operating head of the belt grinding machine comprises two spaced rollers 11 and 12, which are placed one above the other and are substantially parallel one another. An endless abrasive belt 13 is wound between the rollers. The lower roller 11 is a drive roller and the upper roller 12 is a tensioning roller.

Spaced apart from the abrasive belt and proximate an edge thereof, a position sensor 14 is arranged for sensing the position of the abrasive belt. The position sensor 14 used in the present invention is an optical sensor, or the like, having a fork shape or other operatively equivalent shape, whereby a gap is defined between the prongs of the fork-shaped sensor for receiving an edge portion of the belt. An example of optical sensor that may be used in the present invention is the model OGU 050/20 IP3K-IBS manufactured and marketed by DI-SORIC GmbH & Co., or another optical sensor with similar characteristics.

The position of the abrasive belt sensed by the position sensor 14 is transmitted, through a closed loop control circuit of conventional kind, to an electric actuator, illustrated in FIG. 2, which adjusts the position of one of the supports of the tensioning roller 12, in dependence of the position of the abrasive belt being sensed by the position sensor 14.

The electric actuator consists of an electric drive. The electric drive includes a drive shaft and is provided with an angular position transducer allowing the determination of the exact angular displacement of the drive shaft and, thereby, the amount of shifting movement imparted to the adjustable support of the tensioning roller. The drive shaft of the electric drive is connected to a gear reduction unit 16 which transmits the shifting movement to said adjustable support of the tensioning roller in a direction perpendicular to the principle axis of the roller.

The device configured as described above is capable of sensing the position of the abrasive belt with a resolution of 0.1 mm and, by means of the electric motor-gear reduction unit connected to said one of the supports of the tensioning roller, the device allows the position of the abrasive belt to be adjusted by ±2 mm, with a continuous angular correction in dependence of the sensed position of the abrasive belt.

With respect to other known solutions, the device according to the inventions has the following advantages. A first advantage is that the device allows the tensioning roller to be moved by extremely small and precise amounts, thus keeping the abrasive belt practically on track while it rotates. A second advantage consists in that the control of the position of the abrasive belt is not influenced by the direction of rotation of the abrasive belt relative to direction of feed of the workpieces. A third advantage is that the controlled movement of the abrasive belt can be adjusted in amplitude and in frequency.

Finally, it should be noted that the device according to the invention for controlling the position of an abrasive belt is applicable to all kinds of belt grinding machines of the type equipped with operating heads for operation either with or without water, oil or water/oil emulsion coolant. 

1. A belt grinding machine tool with an operating head comprising an endless abrasive belt wound and stretched between at least two spaced rollers arranged parallel one another, of which a first is a driving roller and a second is a tensioning roller, said tensioning roller being supported to be adjustable in a direction which is substantially perpendicular to its axis of rotation, a device for controlling the position of said abrasive belt consisting of at least a position sensor for sensing the position of the abrasive belt and at least an actuator for adjusting the position of the tensioning roller, in dependence of the position of the abrasive belt being sensed by said position sensor, wherein the position sensor is a fork shaped optical sensor, or an optical sensor having an operatively equivalent shape, and said actuator is an electric drive.
 2. A belt grinding machine tool according to claim 1, wherein said electric drive comprises a drive shaft and an angular position transducer for determining amount of rotation of said drive shaft.
 3. A belt grinding machine tool according to claim 2, wherein a gear reducing unit is operatively connected to said drive shaft of the electric drive.
 4. A belt grinding machine tool according to claim 1, wherein said position sensor and said electric drive are operatively connected together through a closed loop control circuit which determines the amount of shifting movement to be imparted to the said tensioning roller as a function of the position of the abrasive belt sensed by said position sensor.
 5. A belt grinding machine tool according to claim 4, wherein the position of said abrasive belt is controlled by said closed loop control circuit in continuous manner, in dependence of the position of said abrasive belt sensed by said position sensor.
 6. A belt grinding machine tool according to claim 1, wherein said operating head is intended for operation either with or without water, oil or water/oil emulsion coolant. 